<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8" />
    <title>2.用watch写姓名案例</title>
    <!-- 引入Vue -->
    <script type="text/javascript" src="../../js/vue.js"></script>
  </head>
  <body>
    <!-- 准备好一个容器-->
    <div id="demo">
      姓：<input type="text" v-model="firstName"> <br>
      名：<input type="text" v-model="lastName"> <br>
      全名：<span>{{fullName}}</span>
    </div>

    <script type="text/javascript">
      new Vue({
        el:'#demo',
        data:{
          firstName:'zhang',
          lastName:'san',
          fullName:''
        },
        watch:{
          // 监视“姓”，只要姓一变，全名就变
          firstName(value){
            this.fullName = value + '-' + this.lastName
          },
          // 监视“名”，只要名一变，全名就变
          lastName:{
            immediate:true,
            handler(value){
              this.fullName = this.firstName + '-' + value
            }
          }
        }
      })
    </script>
  </body>
</html>